Both my preemies were different, my first one didn't ever do that. But my second, who spend 4 months in the NICU did. The first few times I flew out of bed in the middle of the night convinced there was something wrong only to find him sound asleep. The only saving grace is for a preemie it's normal and my son did grow out of it.

My little girl would cry in her sleep also. The question is how long has he been home. I never noticed in the hospital but when she came home I noticed. The Dr. told me that it was normal and that we never noticed it before because the NICU is so loud. I hope this helps make you feel a little better. If you are really concerened call you ped. and ask they will settle you worry.